The present invention relates generally to ink reservoirs for high speed computer driven inkjet printers and plotters and other applications where precise pattern dispensation of a fluid is required such as in the layout of circuit masks. In such printers the ink reservoir is ordinarily maintained under a sub-atmospheric or negative pressure so that ink will not leak or drool from the print head. Various types of ink reservoirs may be used including refillable ink reservoir cartridges which are mounted on the moveable printer carriage, throwaway replaceable cartridges which are mounted on the printer carriage and remote or offboard ink reservoirs from which ink is brought to the print head on the printer carriage by tubing. In the onboard refillable or throwaway cartridges, a polymer foam is ordinarily provided in the ink reservoir so that the capillary action of the foam will prevent ink from drooling from the print head. Polymeric foams of the type typically used for this purpose are non-biodegradable and thus cause environmental problems whenever a previously used cartridge is emptied and thrown away. In addition, the use of industrial foam in the ink reservoir restricts the operating pressure range of the ink cartridge and such foams ordinarily leave a chemical residue which is incompatible with and/or reacts adversely with printer ink. Similarly, the relatively long tubing used to convey ink from an offboard pressure reservoir to a printing head is not easily adaptable to deliver ink to the print head at different printing pressure ranges.
A collapsible ink reservoir for a handheld inkjet printer is disclosed in U.S. Pat. No. 4,422,084 issued Dec. 20, 1983 to Saito. Negative pressure is maintained in a polypropylene ink bag by various types of springs which bias the bag walls apart from each other. The springs may be mounted inside of or externally of the ink bag but the spring pressure regulator construction does not result in substantially complete emptying of the ink bag and the bag itself is not carried on a printer carriage.
Another ink reservoir which achieves constant negative back pressure through an external spring or an elastomeric bladder is disclosed in U.S. Pat. No. 4,509,062 issued Apr. 2, 1985.
One example of an improved onboard ink pressure reservoir cartridge is disclosed in U.S. patent application Ser. No. 07/717,735 filed Jun. 19, 1991 entitled SPRING-BAG PRINTER INK CARTRIDGE WITH VOLUME INDICATOR filed by David S. Hunt and W. Bruce Reid and assigned to the assignee of the present invention. The cartridge disclosed in that application basically comprises a rectangular housing containing a flexible bag of ink, an ink filter and a print head which receives ink from the filter. A spring inside of the bag of ink urges its flexible walls apart from each other thus maintaining a negative or sub-atmospheric pressure in the reservoir which is overcome as ink is emitted from the printhead. As seen in that application, the spring essentially consists of a pair of spaced parallel plates which are urged apart by a spring.
Also of interest are prior co-pending U.S. patent applications Ser. No. 07/929,615 filed Aug. 12, 1992 by Kaplinsky, et al titled COLLAPSIBLE INK RESERVOIR STRUCTURE AND PRINTER INK CARTRIDGE and Ser. No. 07/928,811 filed Aug. 12, 1992 by Khodapanah, et al, titled INK PRESSURE REGULATOR FOR A THERMAL INK JET PRINTER, both owned by the assignee of the present application and incorporated by reference herein.
Further developments of this collapsible bag technology are disclosed in the United States patent application filed on the same day as this application titled LAMINATED FILM INK RESERVOIR by Joseph Scheffelin, owned by the assignee of the present application and incorporated by reference herein.
In collapsible ink bag reservoirs of the type which employ regulator springs inside of thin wall flexible bag walls, it has been found that despite careful handling and packaging, the relatively rigid pressure regulator sideplates may, during shipment or installation puncture the flexible membranes. Although such puncturing is quite rare, this cutting or puncturing must be totally avoided yet this objective must be accomplished without unduly thickening the bag walls so that ink can still be substantially completely exhausted from the collapsible reservoir. In some instances, the regulator springs and their side plates may shift into a skewed position due to shock or vibration. This further increases the risk of unused ink remaining in the reservoir or of damaging contact with the flexible membranes.